Theodore or Walter

This is my first post, but I am desperate for help and am a long time reader of the Nameberry forums. We have a 2 year old daughter named, AdelineElizabeth, and are expecting our second peanut in July. We didn't find out the gender so we're trying to decide on a boy and a girl name front runner. Our two favorites are Theodore and Walter (I slightly prefer Theodore and my husband slightly prefers Walter). With either choice, the middle name will be Justus (my dad's name) and we will call our son by a nickname 99% of the time--Walt or Wally for Walter and Teddy, Ted, or Theo for Theodore. So what do you think? Which full name and then also which nickname should we use for that full name? Urg, this is hard and it is stressing me out because I am constantly going back and forth! Thanks so much for any comments/opinions/advice!

Thanks so much for the responses/votes! I'm surprised how much Theo has pulled ahead. It's my favorite nickname as well, but I was afraid it didn't go that well with Adeline (maybe I thought it sounded too newish?).